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Alteration processes of carbonaceous chondrite parent bodies

碳质球粒陨石母体的蚀变过程

基本信息

批准号：
06403001
负责人：
TOMEOKA Kazushige
金额：
$ 17.41万
依托单位：
Kobe University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1996
项目状态：
已结题

项目摘要

(1) Various types of dark inclusions (DIs) in CV chondrites have been studied in detail by using scanning electron microscopy equipped with an energy dispersive X-ray spectrometer. DIs have been been thought to be primary aggregates of condensates from the solar nebula. However, from all the DIs studied our study revealed evidence that they were affected by aqueous alteration and stbsequant dehydration on the meteorite parent body. The compositional and mineralogical features of DIs indicate that they were probably derived from their host CV chondrites. These results suggest that water and heat source existed in the CV parent body and that aqueous alteration and thermal metamorphism occurred actively.(2) Ca-Al-rich inclusions (CAIs) in four Antarctic CO3 chondrites and four non-Antarctic CO3 chondrites have been studied in detail. Nepheline was found to occur in CAIs in all the CO3 chondrites. Nepheline is formed by replacing mainly melilite and anorthite, indicating it to have an alte … More ration origin. Previously the alteration was thought to have occurred by reaction with the solar nebular gas before accretion. Our study shows that the amount of nepheline increases in the same order as that of metamorphic grade of the CO chondrites. This result suggests that the alteration of CAIs is related to the metamoprhism of the host meteortes, thus it occurred on the meteorite parent body rather than in the solar nebula.(3) In order to better understand the aqueous alteration processes and conditions, we did hydrothermal alteration experiments of the Allende CV3 chondrites. Various alteration mineralogy and textures were produced that resemble those in CI and CM chondrites. Based on the results, we can understand the details of mineralogical and chemical changes that occurred during aqueous alteration of the meteorites.(4) In order to gain our knowledge about the shock histroy of carbonaceous chondrites, we performed shock recovery experiments of the Murchison CM,Yamato 791717 CO and Allende. CV chondrites and studied the recovered samples in detail by using a scanning electron microscope. The meteorite samples were shocked at 5,10,20,25,30,35, and 40 GPa. The carbonaceous chondrites of type CM and CO have not experienced shock pressures higher than 25 GPa. The experimental results indicate that chondrules were flattened at pressures higher than 10 Gpa. The degree of chondrule flattening increases in accordance with the intensity of shock pressure. The experiments also reveal mineralogical and chemical changes that occur in the pressure range between 20 and 40 GPa. Less

(1)用配有能谱仪的扫描电子显微镜对球粒陨石中的各种暗色包裹体进行了详细的研究。DIS一直被认为是太阳星云凝聚物的主要聚集体。然而，从所有的研究中，我们的研究揭示了它们受到了陨石母体上的水蚀变和持续脱水的影响。DIS的成分和矿物学特征表明，它们可能来自其寄主CV球粒陨石。这些结果表明，CV母体中存在水源和热源，水蚀变和热变质作用活跃。(2)对4个南极CO3球粒陨石和4个非南极CO3球粒陨石中的富钙铝包裹体(CAI)进行了详细研究。在所有的CO3球粒陨石中都发现霞石存在于CaI中。霞石主要由黄长岩和斜长岩交代而成，表明其具有阿尔特…。更多的配给来源。此前，这种变化被认为是在吸积之前与太阳星云气体发生反应而发生的。我们的研究表明，霞石的数量与CO球粒陨石变质程度的增加顺序相同。这一结果表明，CAIS的蚀变与宿主陨石的变质作用有关，因此它发生在陨石母体上，而不是发生在太阳星云中。(3)为了更好地了解水蚀变过程和条件，我们对Allende CV3球粒陨石进行了热液蚀变实验。产生了与CI和CM球粒陨石相似的各种蚀变矿物学和结构。(4)为了了解碳质球粒陨石的冲击历史，我们对Murchison CM、Yamato 791717 CO和Allende进行了冲击恢复实验。CV球粒陨石，并用扫描电子显微镜对回收样品进行了详细研究。陨石样本在5、10、20、25、30、35和40 Gpa的压力下受到冲击。CM型和CO型碳质球粒陨石未经历过高于25 Gpa的冲击压力。实验结果表明，在高于10 Gpa的压力下，球粒被压扁。球粒的扁平度随冲击压力的增大而增大。这些实验还揭示了在20到40 Gpa的压力范围内发生的矿物学和化学变化。较少